More Schist and More

I know it's enough already with the schist, but it's not as simple as I thought to identify.

Schist: "A coarse-grained metamorphic rock that consists of layers of minerals and can be split into think irregular plates - from Greek 'skhistos' - to split"



Gneiss: " A metamorphic rock with a banded or foliated structure, typically coarse-grained and consisting mainly of feldspar, quartz and mica - from Old High German 'gneisto'- to spark"



Okay, these are the same rocks it seems to me, I get confused most of the time. The minerals in schist are also mainly mica, quartz and feldspar. Plus maybe some graphite, hornblende, talc and chlorite.

But here's some good news:

"Gneiss resembles schist, except that the minerals are arranged into bands. Sometimes it is difficult to tell the difference between gneiss and a schist because some gneiss appears to have more mica than it really does. This is especially true with mica-rich parting planes."

Most of Manhattan has a bedrock of schist and the Bronx has gneiss.

A glacial erratic is a chunk of rock that is not native to the environment in which it finds itself. It was dragged and dumped there by when the glacier retreated. Erratics can be found hundreds of miles from their home. Poor things. Or maybe they wanted to get away anyway.

When Central Park was constructed in the late 19th century, many of erratics were removed (hopefully shipped back home), but some remain. This one was obvious, but I'll have to find more.